Our goal is to understand the fundamental electronic structure of paramagnetic metal and free radical proteins, to understand the interaction between naturally occuring paramagnetic centers in proteins, and to probe the dynamics of paramagnetic center motion. The outcome of the proposed work will be a more complete understanding of how the paramagnetic centers perform in their biological roles. The specific goals of the proposed research will be: 1. To study Cytochrome P-450 by electron nuclear double resonance (ENDOR) to determine its heme ligand environment. 2. To study by ENDOR the electronic structure at porphyrin-linked nitrogens and protons in ferric hemoglobins, coboglobins, and nitrosyl hemoglobins in order to detect effects of conformational change. 3. To probe by ENDOR the environs of the EPR-detectable "copper" and heme in cytochrome c oxidase and to discover the nature of the ubisemiquinone radical in a newly found radical-ubiquinone protein of the electron transport chain. 4. To probe with pulsed EPR and saturation transfer EPR for evidence of inter-metal interaction and inter-metal distances in cytochrome c oxidase. 5. To look for the effect of slow molecular motions of O2 bound to coboglobins and of the ubiquinone in its protein environment. Pulsed EPR and saturation transfer EPR will be used. To perform these experiments we presently have a working ENDOR spectrometer and modicications for saturation transfer EPR. A pulsed saturation recovery apparatus is now being built to monitor electron spin-lattice relaxation, and a magnetic field pulsing device to operate in conjunction with it will be built as a part of the proposed work.